In the field of integrated circuits, single event upsets (SEU), in which charge stimulated or induced by external radiation is deposited on a node within a latch and causes the latch to switch state, have become more important as transistor size has decreased. The most troublesome charged particles are alpha particles because of their high ionization rate.
Many approaches to the problem have been attempted, depending on the technology; CMOS, emitter coupled logic (ECL), or cascode current switch (CCS), each approach depending on the particular circumstances of the technology in question.
In general, solutions use redundancy or change the gain around the loop t absorb induced charge. In a redundant approach, two latches are connected together, so that the latch will be inverted only when both of the two circuits suffer an alpha-particle strike at the same time. One partial redundant approach, illustrated in Japanese patent 62-81113, takes advantage of extra emitter-follower transistors available in an ECL latch to provide protection for only one of the two storage nodes. This approach is not possible for CCS latches without paying a substantial penalty in increased parts count because the extra emitter-follower transistors are not present. In the gain-modification approach, additional resistance or capacitance is used to absorb the charge induced by the radiation before a transistor can switch state. In the first case, the latch is essentially immune to SEU, while in the second case, the latch is still susceptible to SEU, but only when the charge exceeds some threshold critical charge.